In a recent trend of miniaturization of a semiconductor device, a processing technology having a high degree of accuracy on a semiconductor wafer is required. For performing a high accuracy microprocessing on the semiconductor wafer, e.g., a plasma etching processing, a magnetron type parallel plate plasma processing device has been commonly used.
FIG. 13 offers a schematic configuration of a magnetron type parallel plate plasma processing apparatus of a conventional art.
As shown in FIG. 13, a plasma processing apparatus 80 includes a processing container 81, and the processing container 81 contains an upper electrode 82 and a lower electrode 83 in a top part and a lower part thereof, respectively, wherein the lower part has a mounting surface in a top part thereof, on which a semiconductor wafer W as an object to be processed is mounted. The processing container 81 contains in the vicinity of the top part of the lower electrode 83 a separator 86 for dividing an inside of the processing container 81 into a processing region 84 and an exhaust region 85. The upper electrode 82 has a plurality of gas inlet holes (not shown) for introducing a processing gas into the processing region 84. The separator 86 has a plurality of gas passage holes 86a penetrating through the processing region 84 and the exhaust region 85 such that the processing gas inside the processing region 84 is exhausted to the exhaust region 85.
In the plasma processing apparatus 80, a high density plasma is produced in the processing region 84 into which the processing gas is introduced through the gas inlet holes formed in the upper electrode 82 by a high frequency field and a parallel field, wherein the high frequency field is excited between the upper electrode 82 and the lower electrode 83 by a high frequency power source (not shown) connected to the lower electrode 83 via a matching circuit, and the parallel field is generated by an annular permanent magnet 87 disposed around an upper part of the processing container 81.
FIGS. 14 through 16 explain processing gas flows inside the processing region in the vicinity of the gas passage holes 86a of the separator 86 in FIG. 13.
As shown in FIG. 14, a plasma 40, which is generated by the high frequency field excited between the upper electrode 82 and the lower electrode 83 and the parallel field normal to the high frequency field, is produced in the processing region 84, and a sheath 45 is formed in the vicinity of the separator 86 to thereby generate a sheath field 44. The plasma 40 is formed of neutral gas particles 41, positive charged particles 42, and negatively charged particles 43. Meanwhile, in contrast with FIG. 14, under a common condition (not shown) where there is no electrical or magnetic restriction for charged particles, the charged particles have same movements as the neutral gas particles 41 to thereby be exhausted through the gas passage holes 86a together with the neutral gas particles 41. As a result, a leakage of the plasma 40 from the separator 86 to a manifold part (exhaust region 85) occurs. Due to the leakage of the plasma 40 to the manifold part, inner wall components of the manifold part are eroded, so that a lifetime of the plasma processing apparatus 80 is shortened. And, at the same time, there is a difficulty in controlling an inner pressure of the processing region 84 by way of a CM for pressure control, which is disposed in the manifold part, since it is difficult to keep a pressure of the manifold part constant.
When the positively charged particles 42 and the negatively charged particles 43 move in a same direction, the plasma 40 is ambipolarly diffused. Therefore, the leakage of the plasma 40 can be prevented by suppressing movements of either the negatively or the positively charged particles. As a method thereof, a method for providing a barrier by making the gas passage holes 86a small by employing an electric field formed on the separator 86 has been disclosed.
However, a suppressing efficiency of the leakage of the plasma 40 to the exhaust region 85 is inversely proportional to an exhaust efficiency of the processing gas inside a processing region in the processing region 84. And, as shown in FIG. 15, if a diameter of the gas passage hole 86a is small, the leakage of the charged particle is prevented, resulting in preventing the leakage of the plasma 40. However, the neutral gas particle 41 is not allowed to penetrate through, so that the processing gas inside the processing region 84 cannot be exhausted. On the other hand, if a diameter of the gas passage hole 86a is large, as shown in FIG. 16, the leakage of the plasma 40 to the exhaust region 85 cannot be prevented since there is a difficulty in keeping equipotential surfaces of the sheath field 44 in parallel to a processing-region surface 20a of the separator 86.
For allowing the neutral gas particle 41 to penetrate through and keeping the equipotential surfaces of the sheath field 44 in parallel to the processing-region surface 20a of the separator 86, as shown in FIG. 14, a diameter of the gas passage hole 86a of the separator 86 must be set within a proper range.
However, the proper range in the diameter of the gas passage hole 86a shown in FIG. 14 is too narrow and varies depending on a condition of the plasma 40, so that the diameter of the gas passage hole 86a cannot be set properly and it is difficult to reliably exhaust the processing gas inside the processing region and at the same time securely suppress the leakage of the plasma.
An object of the present invention is to provide a plasma processing device and a baffle plate thereof capable of improving an exhaust efficiency of a processing gas in a processing region and certainly suppressing a leakage of a plasma.